The LCD (Liquid Crystal Display) possesses many advantages of being ultra thin, power saved and radiation free. It has been widely utilized in, such as mobile phones, Personal Digital Assistant (PDAs), digital cameras, laptop screens or notebook screens.
Generally, the liquid crystal display comprises a shell, a LCD panel located in the shell and a backlight module located in the shell. Particularly, the structure of the liquid crystal panel mainly comprise a TFT Array Substrate (Thin Film Transistor Array Substrate), a CF (Color Filter) and a Liquid Crystal Layer. The working principle is that the light of backlight module is reflected to generate images by applying driving voltages to the two glass substrate for controlling the rotations of the liquid crystal molecules.
With the mobile display technology has been playing a significant role in the application of life, the development direction of the mobile display technology goes for higher display quality, high precision degree, thinner and lower power consumption. The size of the element is demanded to be smaller and smaller. The electric field strength in local area inside the element is also enhanced thereby, and particularly, a strong electrical field exists around the drain. Under the action of the strong electrical field, the carrier gains higher energy and becomes hot carrier. The influence of the hot carrier to the element property shows in the following two aspects:
(1) the hot carrier crossing the isolation layer is implanted into the oxide layer and accumulates constantly to change the threshold voltage, and thus affect the element lifetime.
(2) in the depletion region around the drain, new electron hole pairs are generated due to the collision with the crystal lattice. The Metal Oxide Semiconductor (MOS) field effect transistor is illustrated, the electrons generated by collision form the additional leakage electrical current, and holes are collected by the substrate to form the substrate current. The total current becomes a sum of saturated drain current and substrate current. The hot carrier effect is one of the fundamental factors restricting the highest working voltage of the element.
For solving the influence of the appearance of the hot carrier effect to the element property, the technical staff figures out kinds of methods to avoid the generation of the strong electrical field. Please refer to FIG. 1, which is a diagram of a TFT substrate structure according to prior art. The TFT substrate structure comprises a substrate 100, a semiconductor layer 200 positioned on the substrate 100, a source/a drain 300 positioned on the semiconductor layer 200, an insulative layer 400 positioned on the source/the drain 300 and the semiconductor layer 200, and a gate 500 positioned on the insulative layer 400. Specifically, the semiconductor layer 200 comprises a channel area 210 under the gate 500 correspondingly, two n-type heavy doping areas 220 at two sides of the channel area 210 and contacting with the source/the drain 300, and two off set areas 230 among the two n-type heavy doping areas 220 and the channel area 210. Because the offset areas 230 are not doped, and the resistance value is higher, it can disperse the strong electrical field around the electrode to avoid the generation of the hot carriers. However, the leakage current of such kind of TFT substrate structure becomes smaller, and the working current correspondingly becomes smaller, either. It results in the increased power consumption.